There are two basic ways to insulate a finished attic.
Insulating finished attic knee walls.
Blown insulation in the knee wall and top attics.
If only the living space will be insulated wrap the insulation around the room s walls and ceiling and then continue along the floor of the non living space.
How to insulate knee walls.
Unlike traditional walls with two finished sides.
1a attic access door.
In this case the area behind the knee wall will be uncomfortably hot or cold.
The sloped roof creates a small space that can hardly be use.
Kneewalls short walls under sloped ceilings are common in story and a half homes and in bonus rooms above garages.
In finished attic rooms with or without dormer insulate 2a between the studs of knee walls 2b between the studs and rafters of exterior walls and roof 2c and ceilings with cold spaces above.
Knee walls are half walls built into areas where a full sized wall will not fit such as finished attic crawlspaces.
We prefer cellulose but we use fiberglass sometimes too.
2d extend insulation into joist space to reduce air flows.